Oil pumping rigs such as disclosed in U.S. Pat. No. 6,655,224 (2003) to Ji et al. have a wrist pin-shown in FIG. 1 as prior art. These pins wear out and must periodically be replaced. Usually the crank arm is removed from the rig for this operation. Historically a twenty-pound sledge hammer is manually swung against the old stuck wrist pin.
Known in the art is a black powder cannon that may be used to unseat a wrist pin in place on the rig, which may present risks to the worker.
The closest prior art known is shown in FIGS. 2, 3, 4 and 6. An American International Manufacturing Corporation Wrist Pin Knocker is shown. The parts list follows below:
ItemQtyDescriptionPart No. 11Cylinder70362 21Warning Decal70077 31Swivel Nut70401 41Cylinder Head64317 51Aspirator Body64319 6A1Hammer used as valve handle64411 6B1Hammer 71Aspirator Nozzle64320 81Valve Guard64318 9Not Used101Valve Body64415111Pipe Union .75″ NPT64387121Hose Nipple .75″ NPT64383131Adapter 3″- 6 Thd & 3″-8 Thd69975141Hose Clamp No. 10464368151Outer Filter Retainer64360164Hex, Sckt, Screw 3.21 × 1.7564379171Pipe Plug .5070370184Nylock, Hex Nut, 5/16-18 unc64366
The swivel nut 3 is screwed onto an adapter that is screwed onto an end of the stuck wrist pin. The wrist pin knocker is ready when the piston P is set at the swivel nut end. Then the 100 to 125 PSI air hose is connected to the hose nipple 12. Next a control handle 6A (also used as a hammer) is set to the return position→to draw via suction the piston P to the valve guard 8 end. Next the handle is set to the neutral N position. Next the handle is quickly moved to the forward position←which causes the piston P to hit the stuck wrist pin. This operation is repeated until the wrist pin is loosened. The hammer 6A can function as the handle H.
In practice with the one old unit on hand the return function did not work. Instead the swivel nut 3 had to be unscrewed, and the piston P had to be shoved with a stick up to the valve guard 8 end. The cylinder head 4 has a valving assembly that passes compressed air out the aspirator nozzle 7 via a narrow tube 5 in FIG. 2, thereby causing vacuum pressure at the valve guard 8 end for return of the piston P. Air holes in the outer filter retainer 15 in theory allow the piston P to be pulled by vacuum to the valve guard 8 end.
What is needed in the art is an improved piston design that enables the return function as noted above. Further needs are to protect the striking end of the piston P from destroying the inside of the cylinder 1 due to the wobbling of the heavy (twelve pound) steel piston in the aluminum cylinder. Another need is to protect the sliding collars on the piston from wear and tear.
Other needs may include shortening the length of the cannon as well as improving safety by moving the operator away from the cannon as well as providing an adjustable length cannon.
The present invention meets all these needs with an improved piston, a simpler valve assembly, a remote controller, a repositioned controller, and a modular cylindrical shaft.